1. Field of the Invention
The invention relates to a flow meter for measuring the flow rate of a flowing medium, with a plastic measurement tube for routing the medium and a connecting means for connecting one end of the measurement tube to one end of a plastic pipeline.
2. Description of Related Art
Flow meters for measuring the flow rate of a flowing medium are known in diverse versions. Measurement of a volumetric flow is possible, for example, by means of magnetic-inductive flow meters with which the electromagnetic induction of charge carriers moving through a magnetic field is used. The underlying principle of a magnetic-inductive flow meter for flowing media goes back to Faraday who suggested in 1832 that the principle of electromagnetic induction be used for measuring flow velocity.
According to the Faraday induction law, in a flowing medium which is entraining charge carriers and which is flowing through a magnetic field, an electrical field intensity is formed perpendicular to the flow direction and perpendicular to the magnetic field. The Faraday induction law is used in a magnetic-inductive flow meter in that by means of a magnetic coil a magnetic field is generated which has a magnetic field component which runs perpendicular to the flow direction. Within this magnetic field, each volumetric element of the flowing medium which has a certain number of charge carriers and which is moving through the magnetic field with the field intensity which forms in this volumetric element contributes to a measurement voltage which can be tapped via measurement electrodes.
The measurement electrodes in the known magnetic-inductive flow meters are made such that they are coupled either galvanically or capacitively to the flowing medium. Furthermore, one special feature of magnetic-inductive flow meters is the proportionality between the measurement voltage and the flow velocity of the medium averaged over the cross section of the measurement tube, i.e. between the measurement voltage and volumetric flow.
At least in the region of the measurement electrodes, it is necessary for the inner region of the measurement tube to be electrically insulating or to have an electrically insulating lining. To do this, a corresponding insert or a corresponding coating of the measurement tube can be used. However, it is also possible to produce the entire measurement tube from plastic, which simplifies production.
Magnetic-inductive flow meters, but also other flow meters with plastic measurement tubes, are often to be installed in pipeline systems which, likewise, are made of plastic. To do this, screwed or clamped flange connections are often used.
Australian Patents AU 684166 B2 and AU 2483895 disclose connecting two pipelines which have plastic ends and which are used, for example, as pipes for gas or water meters by means of a connecting device, this connecting device producing a corresponding weld/melt connection for this purpose by means of heat, specifically, via corresponding heating wires. Furthermore, Japanese patent application publication JP 2001-349478 A discloses connecting a gas flow meter to a metal pipe via a plastic weld connection.